Conventionally, a radio access system and a radio network that achieves higher-speed data communication (hereinafter referred to as “Long Term Evolution-Advanced (LTE-A)” or “Advanced Evolved Universal Terrestrial Radio Access (A-EUTRA)”) by use of evolution of a radio access system and a radio network in cellular mobile communication (hereinafter referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”), and by use of a wider frequency band than the LTE have been discussed in the 3rd Generation Partnership Project (3GPP).
In the LTE-A, proposed is a reference signal for channel estimation transmitted only when a transmission request is notified from a base station apparatus (A-SRS: Aperiodic Sounding Reference Signal) in addition to a reference signal for channel estimation transmitted at a periodical timing set by the base station apparatus (P-SRS: Periodic Sounding Reference Signal) (non-patent document 1).
[Non-patent document 1] “Channel sounding enhancements for LTE-Advanced”, R1-094653, 3GPP TSG-RAN1 Meeting#59, Jeju, Korea, Nov. 9-13, 2009